1. Field of the Invention
Embodiments of the invention relate generally to hard disk drives (HDDs). More particularly, embodiments of the invention relate to head stack assemblies (HSAS) designed to reduce the amount of off-track displacement of magnetic heads in the HDDs.
2. Description of Related Art
A HDD is a memory device used to provide mass data storage for electronic devices such as personal computers (PCs), MP3 players, mobile phones, and so on. A HDD uses a magnetic head to read and write data on a disk comprising a rotating platter having a magnetic surface. The head is embedded in a head slider, and when the HDD operates, the head slider floats a predetermined distance above the disk. A head stack assembly (HSA) is attached to the head slider to support and move the head slider.
During operation of the HDD, an actuator arm moves the head slider between tracks of the disk containing storage elements. In order to properly read or write data in the storage elements of a selected track, the head slider must be precisely aligned with the track. Unfortunately, however, the HSA or the disk may vibrate due to external disturbances, or due to the operation of a spindle motor of the HDD. Such vibrations may cause the head slider and the associated magnetic head to deviate from a desired position on the selected track. Such deviation is commonly referred to as “off-track displacement” of the head slider or magnetic head.
FIG. 1 is a conceptual diagram used to illustrate off-track displacement of a magnetic head due to mechanical vibrations of a disk platter. The view shown in FIG. 1 is a side-view of the disk platter.
Referring to FIG. 1, a side view of a disk platter 10 in a HDD is shown as a solid box-like shape. Positions of platter 10 during vibrations or other movements are shown as dotted extensions of the solid box-like shape. A head slider 27 of the HDD is illustrated as a small box, and a magnetic head h0 of the HDD is illustrated as a dot on head slider 27.
The position of a track including storage elements to be read by magnetic head h0 is illustrated by a dot on platter 10. In particular, where platter 10 is in a stationary position, the track has a position T(d0); where platter 10 moves upward, the track assumes a position T(d2); and where platter 10 moves downward, the track assumes a position T(d1).
In addition, head slider 27 and magnetic head h0 also assume different positions when platter 10 moves. In particular, where platter 10 is in a stationary position, magnetic head h0 maintains a position h0(d0); where platter 10 moves upward, magnetic head h0 assumes a position h0(d2); and, where platter 10 moves down, magnetic head h0 assumes a position h0(d1).
As illustrated by a vertical line in FIG. 1, the position of magnetic head h0 tends to become misaligned with the track when platter 10 moves. In other words, the movement of platter 10 due to mechanical vibrations or other types of motion tends to cause off-track displacement of head slider 27 and magnetic head h0.
A variety of techniques have been developed in efforts to reduce off-track displacement of head sliders and magnetic heads in HDDs due to mechanical vibrations such as those illustrated in FIG. 1. For example, U.S. Pat. Nos. 6,920,018 and 6,958,879 each disclose a HSA designed to reduce off-track displacement due to disk vibration. In the HDDs disclosed in U.S. Pat. Nos. 6,920,018 and 6,958,879, off-track displacement due to disk vibration is reduced by moving a head slider toward the outer circumference of the platter when the HSA moves downward, and moving the head slider toward the center of the platter when the HSA moves upward.
Although the HSAs disclosed in U.S. Pat. Nos. 6,920,018 and 6,958,879 are capable of reducing off-track displacement caused by mechanical vibrations, the HSAs are not as effective at reducing off-track displacement caused by arm bending of the HSAs. The term “arm bending” here refers generally to movements of extended portions of the HSA due to forces such as torque. For instance, a head suspension component or a swing arm of a HSA may move up and down in response to torque induced by lift forces generated by air flow, and torque induced by downward gravitational pull on the HSA and/or externally induced mechanical vibrations.
FIG. 2 is a conceptual diagram used to illustrate off-track displacement of magnetic head h0 shown in FIG. 1 due to arm bending of a HSA including head suspension component 25 and head slider 27. In contrast to FIG. 1, the view shown in FIG. 2 is a top-view of disk platter 10. Accordingly, in FIG. 2, a solid line labeled “T” represents a single track of disk platter 10.
Referring to FIG. 2, where arm bending occurs, head suspension component 25 moves up and down along with head slider 27 and head h0. Accordingly, magnetic head h0 attached to head slider 27 is displaced relative to track “T”.
More particularly, where head suspension component 25 moves upwards, magnetic head h0 moves from a resting position h0(a0) to a position h0(a1) towards the outer circumference of platter 10. On the other hand, where head suspension component 25 moves downwards, magnetic head h0 moves from resting position h0(a0) to a position h0(a2) towards the center of platter 10.
Because conventional techniques fail to adequately address off-track displacement caused by arm bending, the performance of the HDD may suffer.